10 Be in late deglacial climate simulated by ECHAM5-HAM – Part 2: Isolating the solar signal from 10 Be deposition

• Published in: Climate of the Past
• Main Authors: U. Heikkilä, X. Shi, S. J. Phipps, A. M. Smith
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2014
• Subjects: Environmental pollution; TD172-193.5; Environmental protection; TD169-171.8; Environmental sciences; GE1-350; Greenland; Law Dome; Antarc*; Antarctica; GRIP; Sea ice
• Online Access: https://doi.org/10.5194/cp-10-687-2014; https://doaj.org/article/e3685fd9c34d4c8297083adbc0de87a6

This study investigates the effect of deglacial climate on the deposition of the solar proxy 10 Be globally, and at two specific locations, the GRIP site at Summit, Central Greenland, and the Law Dome site in coastal Antarctica. The deglacial climate is represented by three 30 year time slice simulations of 10 000 BP (years before present = 1950 CE), 11 000 and 12 000 BP, compared with a preindustrial control simulation. The model used is the ECHAM5-HAM atmospheric aerosol–climate model, driven with sea-surface temperatures and sea ice cover simulated using the CSIRO Mk3L coupled climate system model. The focus is on isolating the 10 Be production signal, driven by solar variability, from the weather- or climate-driven noise in the 10 Be deposition flux during different stages of climate. The production signal varies at lower frequencies, dominated by the 11 year solar cycle within the 30 year timescale of these experiments. The climatic noise is of higher frequencies than 11 years during the 30 year period studied. We first apply empirical orthogonal function (EOF) analysis to global 10 Be deposition on the annual scale and find that the first principal component, consisting of the spatial pattern of mean 10 Be deposition and the temporally varying solar signal, explains 64% of the variability. The following principal components are closely related to those of precipitation. Then, we apply ensemble empirical decomposition (EEMD) analysis to the time series of 10 Be deposition at GRIP and at Law Dome, which is an effective method for adaptively decomposing the time series into different frequency components. The low-frequency components and the long-term trend represent production and have reduced noise compared to the entire frequency spectrum of the deposition. The high-frequency components represent climate-driven noise related to the seasonal cycle of e.g. precipitation and are closely connected to high frequencies of precipitation. These results firstly show that the 10 Be atmospheric production signal is ...